What would I discover if I constructed a 20 pound transformer from solid iron

Thread Starter

Hamlet

Joined Jun 10, 2015
524
Heh-heh.

Ive looked, but am unable characterize the losses for doing such a foolish thing.

What kind of loss is one to expect between two identical transformers, one with
laminations, and anther constructed with a solid core?

For the time being, let's assume both cores are made from transformer/silicon steel.

Is the solid-core transformer going to blow-up, rapidly overheat, be 10% less efficient, 50%?

I would expect the solid-core transformer's secondary voltage would be very spongy/saggy under load.
(that might be worthwhile as a current-limiting feature, although shunts are obviously a better solution.)

What you say?
 

MisterBill2

Joined Jan 23, 2018
19,366
The core of the solid transformer would run quite hot, and the efficiency would be poor. The purpose of using lamanations in a transformer is to prevent current from flowing in the core. That is why the lamanations are thin and have an insulating oxide layer: To reduce currents induced by the changing magnetic field. It would be much cheaper to cast the transformer iron in one or two pieces but it would be much less efficient.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
524
That current in the core is called eddy currents .
Cores made out of high resistance material, such a ferrites, don't need laminations to prevent this current.
Right. I can see it would be a big inductor. I have a current smoother from a hospital that is made from cast iron, same kind of thing.
 

MisterBill2

Joined Jan 23, 2018
19,366
Just because an attempt works does not mean that it is a best choice. And just because a solid core transformer works does not mean the efficiency is even close to adequate.
AND NOBODY SAID that a solid core transformer would not work, only that it was not at all efficient.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
524
Thanks. Just for grins, I have an idea for making a transformer from iron bailing wire, the soft stuff. Either as a torroid, or a bundle, with the ends bent back over the top of the windings, completing the magnetic path. Might not be optimal, but if you can't find what you want at a reasonable price, perfection be damned, do it yourself.
 

MisterBill2

Joined Jan 23, 2018
19,366
It will be a better transformer if you insulate the wire with a coat of paint first. You will need to let it dry completely, though.
Actually, you can wind the iron wire in a loop and build a torroid transformer and be a lot more efficient. Or use rusty wire and it may not need any painting to insulate it. Probably once it is wound it should be wrapped with tape, such as masking tape, both for insulation and for holding the iron wire turns together.
Depending on how you wind the wire, it might even work to wind the core after the coil.
 

MisterBill2

Joined Jan 23, 2018
19,366
I have some of those cores, and what you would discover is that they are not wound after he wire. The iron cores are wound, bonded, sliced, machined and lapped, and paired to assemble with no air gap The joint is usually so perfect that it is difficult to spot.
 

Ian0

Joined Aug 7, 2020
10,232
I have some of those cores, and what you would discover is that they are not wound after he wire. The iron cores are wound, bonded, sliced, machined and lapped, and paired to assemble with no air gap The joint is usually so perfect that it is difficult to spot.
The blurb says that’s how it is done.
I’m cynical about the efficiency, as the comparison is with a EI-laminated transformer. If they were so good, the comparison would be with a toroid.
 

MisterBill2

Joined Jan 23, 2018
19,366
I am very skeptical as to the truth relative to the claim that the cores are wound after assembly. consider the challenge of repeatedly feeding that steel strip thru a constantly narrowing gap, and then pulling it snug. It simply makes no sense that it would be done that way in a profitable manner.
The cores I have, which were produced about 40 years ago, do not appear to have gaps when they are placed together.
I have not yet done the aluminum foil crush test yet to confirm that, but the appearance and feel is that of two llapped surfaces touching.
A video of the machine claimed to do it would be very interesting, also hard to believe.
 

Ian0

Joined Aug 7, 2020
10,232
I am very skeptical as to the truth relative to the claim that the cores are wound after assembly. consider the challenge of repeatedly feeding that steel strip thru a constantly narrowing gap, and then pulling it snug. It simply makes no sense that it would be done that way in a profitable manner.
The cores I have, which were produced about 40 years ago, do not appear to have gaps when they are placed together.
I have not yet done the aluminum foil crush test yet to confirm that, but the appearance and feel is that of two llapped surfaces touching.
A video of the machine claimed to do it would be very interesting, also hard to believe.
I need a transformer about 160VA at the moment (I was going to buy an off-the-shelf toroid) I think I'll request a sample, just to satisfy my curiosity. (And I'll report back!)
 

MisterBill2

Joined Jan 23, 2018
19,366
An off-the-shelf transformer of adequate quality is the best choice. And if the tape wound models perform well, that is good. But it is a challenge to believe that an adequate process for winding a good quality steel core around a plastic bobbin as described is even possible.
 

Ian0

Joined Aug 7, 2020
10,232
An off-the-shelf transformer of adequate quality is the best choice. And if the tape wound models perform well, that is good. But it is a challenge to believe that an adequate process for winding a good quality steel core around a plastic bobbin as described is even possible.
Of course it is, but it is a case of Nullius in Verba. Besides, catalogue companies charge a lot for transformers, and it won't cost me much more even with the carriage from China. Then I'll know if it is any good or not. If not I've got an expensive paperweight, but the odds are it will probably be about as good as an R-core.
This is much the same attitude as the TS. He could buy an iron ring (they are available from welding suppliers for making fancy railings and gates) and he could wind some wire around to see how well it works. It won't cost too much. Though I wouldn't suggest a 230V primary, or it will make his thumbs hurt.
 

MisterBill2

Joined Jan 23, 2018
19,366
I was not by any means suggesting a crude, cobbled up substitute transformer. Not one bit! I am questioning the process of winding a coil of transformer grade steel around a completed set of transformer windings, and the possibility of it being done well at a reasonable production rate.
 
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